Allow post-processors in the core configuration

config.go

@@ -40,9 +40,10 @@ type config struct {
 	PluginMinPort uint
 	PluginMaxPort uint
 
-	Builders     map[string]string
+	Builders       map[string]string
-	Commands     map[string]string
+	Commands       map[string]string
-	Provisioners map[string]string
+	PostProcessors map[string]string `json:"post-processors"`
+	Provisioners   map[string]string
 }
 
 // Decodes configuration in JSON format from the given io.Reader into
@@ -94,6 +95,19 @@ func (c *config) LoadHook(name string) (packer.Hook, error) {
 	return c.pluginClient(name).Hook()
 }
 
+// This is a proper packer.PostProcessorFunc that can be used to load
+// packer.PostProcessor implementations from defined plugins.
+func (c *config) LoadPostProcessor(name string) (packer.PostProcessor, error) {
+	log.Printf("Loading post-processor: %s", name)
+	bin, ok := c.PostProcessors[name]
+	if !ok {
+		log.Printf("Post-processor not found: %s", name)
+		return nil, nil
+	}
+
+	return c.pluginClient(bin).PostProcessor()
+}
+
 // This is a proper packer.ProvisionerFunc that can be used to load
 // packer.Provisioner implementations from defined plugins.
 func (c *config) LoadProvisioner(name string) (packer.Provisioner, error) {

packer.go

@@ -53,6 +53,7 @@ func main() {
 	envConfig.Components.Builder = config.LoadBuilder
 	envConfig.Components.Command = config.LoadCommand
 	envConfig.Components.Hook = config.LoadHook
+	envConfig.Components.PostProcessor = config.LoadPostProcessor
 	envConfig.Components.Provisioner = config.LoadProvisioner
 
 	env, err := packer.NewEnvironment(envConfig)

packer/plugin/client.go

@@ -140,6 +140,18 @@ func (c *Client) Hook() (packer.Hook, error) {
 	return &cmdHook{packrpc.Hook(client), c}, nil
 }
 
+// Returns a post-processor implementation that is communicating over
+// this client. If the client hasn't been started, this will start it.
+func (c *Client) PostProcessor() (packer.PostProcessor, error) {
+	_, err := c.rpcClient()
+	if err != nil {
+		return nil, err
+	}
+
+	// TODO
+	return nil, nil
+}
+
 // Returns a provisioner implementation that is communicating over this
 // client. If the client hasn't been started, this will start it.
 func (c *Client) Provisioner() (packer.Provisioner, error) {